An accurate estimation of maximal voluntary muscle activation is critical for normalisation in scientific studies. Only a handful of studies appropriately normalise muscle activation data when investigating paraspinal muscle activity in populations such as adolescent idiopathic scoliosis (AIS). This neglect compromises the ability to interpret data. The aim of this study was to determine the type of trunk extension task that reliably achieves peak paraspinal muscle activation in participants with and without AIS. Adolescent females with typically developing spines (controls: n = 20, mean[SD] age 13.1[1.8]years), or primary right thoracic AIS (n = 24, age: 13.8[1.5]years, Cobb angle thoracic: 39.5[16.4]°, lumbar: 28.0[11.6]°) performed a series of 3x unresisted and 3x resisted maximal voluntary trunk extensions in prone. Paraspinal muscle activation was recorded bilaterally at two thoracic levels and one lumbar level using surface electromyography (EMG). Muscle activation was highly repeatable within task [ICC 0.77-0.95, all p < 0.01]. At group level, there were no differences in peak muscle activation between tasks irrespective of side (left/right) or vertebral level (Estimate 0.98, 95%CI 0.36 to 2.65, p=0.97). Peak activation was achieved with the unresisted task in 40.5%, and resisted task in 59.5% of the total outcomes (6 recording locations, 44 participants). Individual participant maximum amplitude varied up to 64% (mean[SD]:18[13]%) between the unresisted and resisted tasks. We recommend that both the resisted and unresisted trunk extension tasks are used to increase confidence that a maximum voluntary activation of paraspinal muscles is achieved. Failure to do so could introduce large error in the estimations of muscle activation.
Keywords: Electromyography; Maximal voluntary contraction; Muscle activity; Paraspinal; Trunk extension.
Copyright © 2024. Published by Elsevier Ltd.